Bacteriophage CE6 is a recombinant lambda phage containing the T7 RNA polymerase gene (Studier 1986). The polymerase gene is cloned into the int gene, such that it is transcribed from the p_L and p_I promoters of the phage during infection. λCE6 can be used to provide a source of T7 RNA polymerase to susceptible host cells carrying T7 expression plasmids. In general, it is used when a target gene is so toxic that the plasmid cannot be maintained in DE3 lysogenic hosts, or with alternative hosts that are not DE3 lysogens. The phage has λcI857 immunity and the Sam7 mutation, which requires supF hosts for lytic growth (neither lytic growth nor different immunity are required for T7 RNA polymerase synthesis). It is provided as a high titer lysate and includes host strains LE392 (r_K12^– m_K12⁺) and ED8739 (r_K12^– m_K12^–) as glycerol stocks. The 10-ml size is enough to induce up to 100 ml culture.